Temperature when tapping vs. splits on tree

[WestfordSugarworks]

Anyone have any links to research publications regarding tree damage vs. temperature when tapping? A lot of people have different temps at which they will or won't tap, but i'm wondering if there is any well researched evidence that shows that tapping below a certain temperature is more likely to split a tree. Also, anoyne know what kind of damage a split does to the tree? From what I know about trees and the cracks that I've seen, it doesn't seem like cracks go very deep and thus wouldn't damage the cambium or the xylem. It seems like no matter the temperature, you will get a few split trees and these trees seem to do just fine in our woods. I'm not talking about splits from driving the spout in with extreme force, just splits that may develop a few days or more after tapping. If there is no real damage to the tree from splits, why worry about them? I don't know..

[Bucket Head]

I do not know if a study about temp. and tapping has ever been done. I know tapping takes place at many different temps. throughout many different months in the Northeast.
My only negative experience with tapping and cracking was with the Leader "shark fin" aluminum bucket spout. If you put one in a drill guide, you'll see that the tapered part is much bigger than 5/16". Not exactly helpful in my opinion. The trouble comes when you tap frozen wood with those. They don't always split, but they split enough to make you wait and tap after the wood thaws. Once the hole splits, most if not all the sap runs down the tree instead of into the bucket. Also not helpful.
The tree heals those splits without trouble, just like the tap hole itself, but it's also the sign of a bad taping job. And the wet bark during the season gives it away too!
Steve